In disc brake assemblies, a rotatable rotor rotates with the axle of a wheel to be braked. Two friction pad structures are disposed on opposite sides of the rotor. Each friction pad structure comprises a steel backing plate and a brake pad. The friction pad structures are moved inwardly, toward one another, under the force applied by a hydraulically-actuated piston and related caliper fingers of a caliper mounting structure. The plates are moved outwardly, away from one another, by return springs.
When the pistons and caliper fingers press the backing plates inwardly, the inner surfaces of the brake pads are engaged in frictional, braking contact with the rotor. A relatively high pitched and undesired brake squeal noise can be produced during such braking engagement of the pads on the rotor. The brake squeal noise is produced by vibration of the friction pad structures during braking actuation.
To reduce the undesired brake squeal noise, sound-dampening shim constructions have been used, both by original equipment manufacturers and by brake repair shops. The sound-dampening shim constructions have been positioned both between the hydraulically-actuated piston and the piston engaging surface of the related steel backing plate, and also between the caliper fingers and the caliper contact surface of the related steel backing plate. One such shim structure is shown in U.S. Pat. No. 5,518,088.
It is desirable to provide an improved apparatus for sound-dampening brake squeal noise in which the brake squeal noise is reduced, and a variety of brake squeal frequencies may be absorbed.